Measurements of binary diffusion coefficients in argon-neon mixtures using a Loschmidt cell combined with holographic interferometry

T. Kugler1,2, M. Rausch1,2, A. Fröba1,2, D. Buttig3,4, E. Bich3, E. Vogel3 and E. Hassel4

1Erlangen Graduate School in Advanced Optical Technologies (SAOT), University Erlangen-Nuremberg, Germany
2Institute of Engineering Thermodynamics (LTT), University of Erlangen-Nuremberg, Germany
3Institute of Chemistry, University of Rostock, Germany
4Department of Engineering Thermodynamics, University of Rostock, Germany

Keywords: Loschmidt cell
property: binary diffusion coefficient
material: gas mixtures

Binary diffusion coefficients in argon-neon mixtures were determined with a newly designed Loschmidt cell combined with holographic interferometry. Measurements were performed between (293.15 and 353.15) K and for pressures ranging from (1 to 10) bars over the complete composition range. The obtained results are compared with available literature data. The vertically oriented Loschmidt cell consists of two identical half cells with rectangular cross sections which can be separated and connected by a slide valve. After opening the slide valve the diffusion process starts and a time-dependent vertical gradient in the molar density of the considered component occurs along the measuring cell. The change in the molar density as a function of time and position leads to a change in the refractive index which is analyzed continuously and simultaneously in both half cells by holographic interferometry. For data evaluation, Fick’s idealized second law is applied. Using pure gases at the beginning of the diffusion process, the dependence of the binary diffusion coefficient on composition can be determined over the complete range of mole fractions performing one single experiment. With this strategy, however, real gas effects like the volume change due to mixing and hence convective mass fluxes have to be taken into account. These effects on the binary diffusion coefficient of the noble gas system argon-neon and the adequacy of using Fick’s idealized second law for data evaluation are discussed. Future prospects are given concerning intended measurements for the system ammonia-helium, which is of great technical interest. As this system features a more pronounced deviation from ideal gas behavior than the noble gas system argon-neon, the need for an extended evaluation strategy is discussed.

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